The present invention relates generally to safety devices for use with electrically operated power devices, such as, tools and machinery, and deals more specifically with apparatus for preventing the start-up of a power device after AC power is restored when the power device is in an "ON" condition.
A very serious and dangerous condition leading to bodily injury can arise from tools and machinery that are controlled by a toggle switch "ON-OFF" that may be operated and left in the "ON" position when AC power to the machine or tool fails. The operator of the machine or tool may not have time or the presence of mind to operate the toggle switch to the "OFF" position before the AC power is restored. Such a sequence may result in the machine or tool restarting at an unexpected time thereby causing injury to the operator or other personnel in the area of the machine. The Occupational Safety and Health Administration "OSHA" has recognized this safety problem and now requires that electrically powered devices with a toggle switch to change the state between an "ON" and "OFF" condition be equipped with a safety device that will prevent the electrically powered device from restarting automatically when the AC power is restored.
Currently known devices generally consist of a relay that has its coil powered by the line voltage through a normally open push button switch and latching circuit. After power is restored, the operator may activate the push switch to provide power to the machine or tool. However, if the toggle switch of the machine or tool is left in the "ON" position, the machine will restart immediately.
Therefore, it is a general object of the present invention to provide a safety device to prevent power from being restored to the machine or tool after AC power is restored when the machine or tool is left in the "ON" condition.
It is a further object of the present invention to provide a safety device that connects and disconnects the power device from an AC power line without switching large line currents thereby reducing the complexity and cost of the safety device.